There is a large and continuing need for identifying and monitoring the level of pollutants (contaminants) in air and in gas streams of, for example, industrial type. This need is often addressed by obtaining a sample of the air/gas at the monitoring site and transporting the sample to a laboratory for analysis. The samples may be obtained by filling (i.e., preferably manually) a sampling holder or container such as a plastic bag, a hypodermic syringe, or an evacuated metal or glass vessel and sealing it for transportation. However, sampling devices that take a bulk air sample for transport and later analysis are often inappropriate for use in circumstances in which the contaminant being monitored is present in small concentrations, in the parts per billion or even parts per trillion range. The size of the sample that is collected is often too small for the contaminant to be detected and its concentration measured. That requirement has led to the development of air/gas sampling devices that preferentially extract and trap the contaminants from the sampled air or gas stream and hold the trapped contaminants for later release and analysis. Air/gas sampling sorbent tubes (or other similar media) are among such devices as the tube or medium contains a sorbent material that functions to extract and hold contaminants from an air/gas stream passing through the tube or over the medium. Because most contaminants of interest are organic compounds, the sorbent material (i.e. sorbents) is chosen to absorb or adsorb those compounds while allowing air/gas and inorganic compounds to pass through the tube substantially unimpeded. There exists a variety of air/gas sampling sorbent tubes or sorptive media which are used to extract and retain volatile organic compounds from air/gas flowing through them during the sampling period for later analytical determination of the volatile organic compounds contained in the air/gas. When such air/gas sampling sorbent tubes are loaded onto an analytical instrument, the retained volatile organic compounds are liberated using desorption or solvent extraction and allowed to flow into the analytical instrumentation. Analysis of the liberated volatile organic compounds is then accomplished using any of several analytical instruments and/or techniques or using a combination thereof.
The foregoing air/gas sampling sorbent tubes require that they be maintained in a contaminant-free condition prior to air/gas sampling at the monitoring site. In this regard, the air/gas sampling sorbent tube may be manufactured to have a body portion containing desired sorbent material and lateral end portions that are either capped with plastic over-caps or screw-threaded end caps. Alternatively, the air/gas sampling tube itself may be formed to be of an integral closed construction having its lateral ends or other enclosure enclosed for a later breakage by a user at a monitoring site to then expose the central body portion containing the desired sorbent material.
In the former case of capped air/gas sampling sorbent tubes or otherwise enclosed sorptive media, the capping of open sorbent tube ends or the capping of the medium may not form a perfect airtight seal and, therefore, may permit the exchange of surrounding air with the air inside the air/gas sampling tube or other sorptive medium. Any volatile or semi-volatile organic compounds contained in the air undesirably passing into the sampling tube or other sorptive medium during storage and/or transport to (and/or from) a monitoring site (or to and/or from a storage site) are adsorbed or absorbed onto the sorbent contained therein and are, during the subsequent analysis, transferred into the analytical instrument and are manifested as interferences, background, or sample overlap. Because of these deleterious analytical errors or the potential thereof, the amount of time that sampling tubes or other sorptive media can be stored prior to actual use at a sampling site is greatly reduced. In addition, the user is afforded no assurance that the sampling tube or other sorptive medium has been stored in a clean environment and is free of contamination.
Thus, it is desirable to provide a sorbent holder system which is able to overcome the above disadvantages.
Therefore, a need exists to provide a sorbent holder system that stores or transports a sorbent holder. Advantages of such a sorbent holder system would, inter alia, include the following:                Protecting the sorbent from undesired contamination during storage of the sorbent holder;        Protecting the sorbent from undesired contamination during transportation of the sorbent holder; and        Enabling increased accuracy of the sorbent analysis due to reduction or elimination of undesired contaminants from the sorbent during storage or transport of the sorbent holder.        
These and other advantages of the present invention will become more fully apparent from the detailed description of the invention hereinbelow.